1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, it relates to a method of manufacturing a semiconductor device wherein a titanium film and a titanium nitride film overlying the titanium film are formed.
2. Description of the Related Art
As also seen in very large scale integration (VLSI), ultra LSI (ULSI), or the like, a proportion occupied by wiring portions tends to increase on a semiconductor device or chip as the device is heightened in the density of integration and is enhanced in functionality. A wiring pitch has been shortened in order to prevent the area of the chip from enlarging due to the increase of the occupied proportion.
In applying a borderless VIA hole to the shortened wiring pitch, there has been adopted a structure wherein a titanium nitride film formed over a lower-layer wiring line and to constitute a cap metal is left in the bottom of the VIA hole at the step of etching the VIA hole. In this case, a wiring line structure wherein a titanium film 112 is sandwiched in between an aluminum-copper alloy film 111 being the material of the lower-layer wiring line and the above titanium nitride film 113 as shown in FIG. 3 of the accompanying drawings, has been usually adopted in order to lower a VIA resistance.
A related art method of forming the titanium film and the titanium nitride film will be explained below. As illustrated in FIG. 4, titanium film and the titanium nitride film to constitute the cap metal are formed by employing a sputtering apparatus in which a chamber 201 for the titanium film and a chamber 202 for the titanium nitride film are disposed separately from each other, and in such a way that, after the titanium film has been formed in the chamber 201, the titanium nitride film is formed in the chamber 202. Alternatively, using a single chamber, not shown, which is furnished with a shutter for cleaning a target surface, only the target surface is cleaned by closing the shutter before the formation of the titanium film, and the titanium film and the titanium nitride film are thereafter formed by sputtering.
The titanium film obtained by the film forming method stated above has a thickness of 5 [nm].about.10 [nm] or so ordinarily, and it is a film of good quality containing nitrogen and the like impurities little.
The wiring line structure obtained by the related art film forming method, however, has a problem as stated below. An aluminum-titanium alloy layer 114 which is produced by the reaction of aluminum and titanium is formed on the aluminum-copper alloy film 111 as shown in FIG. 5, due to a heat treatment at 400.degree. C. or above. The aluminum-titanium alloy layer 114 has been reported to act as the diffusing path of atoms. It forms a cause for the drift of aluminum atoms, and deteriorates an electromigration lifetime.